1. Technical Field
The present invention relates generally to semiconductor fabrication, and more particularly, to methods of preventing damage of a metal during lag times in semiconductor fabrication by using clustered processing and an at least partially sacrificial encapsulation layer.
2. Related Art
During semiconductor fabrication, metal that forms circuitry is formed in various materials. Metals such as copper (Cu) are typically lined with a liner material such as tantalum nitride, which prevents interaction of the metal with other materials. During processing, however, lag times in processing leave the metal exposed. Exposure of the metal to an ambient environment, other materials used in the processing or even adjacent dielectric structure during the lag times can cause damage to the metal. The damaged metal results in yield and reliability problems. Lag times can be created and or extended by a number of situations. For example, lag times may be created between etching steps and encapsulation of the metal with the liner. In addition, other situations such as unplanned tool down times and tool overload increases metal exposure time.
FIGS. 1A-D show one illustrative conventional process including: A) a damascene wire lithography (via first) using a mask 2 through a dielectric 4; B) metal reactive ion etching (RIE), resist stripping and silicon carbide nitrogen etching to reveal metal 6 through cap layer 8; C) a post-RIE wet cleaning; and D) liner 9 deposition. Lag times that may occur are shown in the form of arrows. FIG. 2A shows conventional metal (e.g., copper) damage in terms of corrosion 10; and FIGS. 2B and 2C show metal (e.g., copper) damage in terms of growths 12, 14 of, for example, copper oxyfluoride (CuOF) 14 and ammonium fluoride (NH4F) 12. In either event, the resulting circuitry may exhibit increased via resistance, via opens, wire shorts, and degraded reliability (i.e., via resistance increase during use in the field or increased current leakage between wires). Certain intermetal dielectrics such as fluorinated silica glass (FSG), hydrogenated silicon oxycarbide (SiCOH) and porous-SiCOH especially exhibit increased metal damage.
One approach to address the exposure problem has been to implement exposure time window limitations (e.g., ˜6-24 hours). Time window limitations may be applied to the durations shown by arrows in FIGS. 1A-D. Unfortunately, management of these time window limitations is expensive. In addition, other situations such as unplanned tool down times and tool overload oftentimes result in exceeding the exposure time window limitations. Furthermore, exposure time window limitations may not be adequate because yield and reliability data frequently indicates that metal damage can begin immediately upon exposure, e.g., in less than 1 hour.
In view of the foregoing, there is a need in the art for an improved solution to the metal exposure problem.